ucb dist test3 - rficrfic.eecs.berkeley.edu/142/pdf/distomeaslect.pdfspectrum analyzer basics lets...

Spectrum Analyzer Basics www.agilent.com/find/backtobasics

Agenda

� Overview:

� What do we use to measure distortion

� What is spectrum analysis?

� Theory of Operation:

� Spectrum analyzer hardware

� Specifications:

� Which are important and why?

� Features

� Making the analyzer more effective

� Demo of Intermodulation and Harmonic Meas’ts

� Using a Spectrum Analyzer

�Fixed freq and power

� Using a Network Analyzer

�Swept freq and power

�Gain Compression


What are Distortion Measurements

• Principally, we measure the distortion in terms of the products (signals) that are produced when an active device (amplifier or mixer) is driven in a non-linear mode

• Non-linear means the output power is not a linear function of the input power: The gain is not constant with drive level

• Products (distortion signals) are harmonics (usually tested with a single tone input), or inter-modulation signals, tested with two-tones (or more).

• We might want to test the distortion while changing:

– Frequency

– Power

– Tone-spacing


Amplifiers – Measurement Requirements

• Small Signal Amplifiers Critical Measurements

– Gain

– S-Parameters (S11, S21, S12, S22)

– Output 1 dB Compression (P1dB)

– Output 3rd Order Intercept Point (OIP3)

– Harmonics

– Load Pull

– Hot S22

– Noise Figure


OverviewFrequency versus Time Domain

time

Amplitude

(power) frequenc

y

Time domain

MeasurementsFrequency Domain

Measurements


Lets first look at the effect of change in gain with power level

• Non-linear gain means that the gain changes with power level

• You can test this by sweeping the frequency response, at several

different power levels.

• OR you can see the gain compression effect at one frequency, by

holding the frequency constant, and measuring the gain, or the

output power, while sweeping the input power

• A key figure of merit is P-1dB, or the power that causes the

apparent gain to be reduced by 1 dB


Gain Compression – CW Power Sweep• What can be measured with a CW Power Sweep?

– Gain Vs. Drive

– Requires an Enhanced Response (ER) or a 2-Port Calibration. ER is recommended since amplifier is being driven into compression and the 2-Port correction math does not hold true under non-linear conditions.

– Input Power at P1dB

– Strictly speaking, this only requires a source power cal on the input port and receiver cal for the reference receiver. If corrected Gain numbers are also required, then an ER cal should also be done.

– Output Power at P1dB

– Again strictly speaking, this only requires a receiver power cal on measurement receive port, but this also requires a calibrated source. Also again if corrected Gain numbers are required, then an ER cal should be done.

– Phase Vs. Drive

– This also requires an ER or a 2-port cal. Again, an ER Cal is recommended.

– Combination of All of The Above

– This requires a combination of an ER cal and a measurement receiver cal done in a particular way. The following slides will explain the procedure.


CW Gain Compression Results

Linear Gain

OP1dB

IP1dB

Deviation From Linear

Phase

Gain vs. Drive

Phase vs. Drive

Pin

Pout

• DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz


Finding The 1 dB Compression Point With Markers

• On the gain trace add a reference marker.

• Move the Ref marker to the linear region of the gain trace.

• Add a regular marker to the gain trace and set its property to coupled.

• With the marker selected, go to the Marker Search dialog and choose target search. Set the target to -1 and turn tracking on.

• Your marker will now show the point on the gain trace where the gain is 1 dB less than the linear gain.

• On the other traces in the window add the same marker and choose “Coupled Markers” from the marker dialog. Now all those markers also point to the 1 dB Compression point.


Other distortion characteristics can be viewed using a

Spectrum Analyzer

8563ASPECTRUM ANALYZ ER 9 kHz - 2 6.5 GHz


OverviewTypes of Tests Made .

ModulationModulation

DistortionDistortion

NoiseNoise


OverviewDifferent Types of Analyzers

A

ff1 f2

Filter 'sweeps' over range of

interest

LCD shows full

spectral display

Swept Analyzer


Theory of OperationSpectrum Analyzer Block Diagram

Pre-Selector

Or Low Pass

Filter

Crystal

Reference

Log

Amp

RF input

attenuator

mixer

IF filterdetector

video

filterlocal

oscillator

sweep

generator

IF gain

Input

signal

CRT display


Theory of OperationMixer

MIXER

f sig

LOf

f sig LOf

LOf f sig-

LOf f

sig+RF

LO

IF

input


IF FILTER

Display

Input

Spectrum

IF Bandwidth

(RBW)

Theory of OperationIF Filter


Theory of OperationDetector DETECTOR

Negative detection: smallest value

in bin displayed

Positive detection: largest value

in bin displayed

Sample detection: last value in bin

displayed

"bins"

amplitude


Theory of OperationVideo Filter

VIDEO

FILTER


Theory of OperationOther Components

LCD DISPLAY

SWEEP

GEN

LO

IF GAIN

frequency

RF INPUT

ATTENUATOR


Theory of OperationHow it all works together

3.6

(GHz)

(GHz)

0 3 61 2 4 5

0 31 2

3 64 5

3.6

(GHz)0 31 2

fIF

Signal Range LO Range

fs

sweep generator

LO

LCD display

input

mixer

IF filter

detector

A

f

fLO

fs

fs

fs

fLO-

fs

fLO+

fLO

3.6 6.5

6.5


Theory of OperationFront Panel Operation

8563ASPECTRUM ANALYZ ER 9 kHz - 2 6.5 GHz

RF Input Numeric

keypad

Control functions

(RBW, sweep time,

VBW)

Primary functions

(Frequency, Amplitude, Span)

Softkeys


SpecificationsAccuracy

Absolute

Amplitude

in dBm

Relative

Amplitude

in dB

Relative

Frequency

Frequency


SpecificationsResolution

Resolution

BandwidthResidual FM

Noise Sidebands

What Determines Resolution?

RBW Type and

Selectivity


SpecificationsResolution: Resolution Bandwidth

3 dB3 dB BW

LO

Mixer

IF Filter/

Resolution Bandwidth Filter (RBW)Sweep

Detector

Input

Spectrum

Display

RBW


Demo - Theory: IF filter

ESG-D or DP

Sigl Gen

Spec An

8447F Amplifier

Power Splitter

(used as combine)

inout

ESG-D or DP

Sigl Gen

On

On

Bandpass filter

(center frequency = 170 MHz)f1=170 MHz,

F2=170.01 MHz

A=-25 dBm

fc=170 Mhz

RBW=1 MHz

VBW=300 kHz

Span=10 MHz

Spectrum Analyzer Setup

Signal Generator Setup Filter


SpecificationsResolution: Resolution Bandwidth

3 dB

10 kHz

10 kHz RBW


SpecificationsResolution: RBW Type and Selectivity

3 dB

60 dB

60 dBBW

60 dB BW

3 dB BW

3 dB BW

Selectivity =


SpecificationsResolution: RBW Type and Selectivity

10 kHz

RBW = 10 kHzRBW = 1 kHz

Selectivity 15:1

10 kHz

Distortion

Products

60 dB BW =

15 kHz

7.5 kHz

3 dB

60 dB


SpecificationsResolution: Residual FM

Residual FM

"Smears" the Signal


SpecificationsResolution: Noise Sidebands

Noise Sidebands can prevent resolution of

unequal signals

Phase Noise


SpecificationsResolution: RBW Determines Measurement Time

Penalty For Sweeping Too Fast

Is An Uncalibrated Display

Swept too fast


SpecificationsResolution: Digital Resolution Bandwidths

DIGITAL FILTER

ANALOG FILTER

SPAN 3 kHzRES BW 100 Hz

Typical Selectivity

Analog 15:1

Digital 5:1


SpecificationsSensitivity/DANL

Sweep

LO

MixerRFInput

RES BWFilter

Detector

A Spectrum Analyzer Generates and Amplifies Noise Just Like Any

Active CircuitA Spectrum Analyzer Generates and Amplifies Noise Just Like Any

Active Circuit



10 dB

Attenuation = 10 dB Attenuation = 20 dB

signal level

Effective Level of Displayed Noise is a Function of RF

Input AttenuationEffective Level of Displayed Noise is a Function of RF

Input Attenuation

Signal -To -Noise Ratio Decreases as

RF Input Attenuation is Increased


SpecificationsSensitivity/DANL: IF Filter (RBW)

Decreased BW = Decreased Noise

100 kHz RBW

10 kHz RBW

1 kHz RBW

10 dB

10 dB

Displayed Noise is a Function of IF Filter

BandwidthDisplayed Noise is a Function of IF Filter

Bandwidth


SpecificationsSensitivity/DANL: VBW

Video BW Smoothes Noise for Easier Identification of

Low Level SignalsVideo BW Smoothes Noise for Easier Identification of

Low Level Signals



Signal

Equals

Noise

Sensitivity is the Smallest Signal That Can Be

MeasuredSensitivity is the Smallest Signal That Can Be

Measured

2.2 dB


SpecificationsDistortion

Two-Tone Intermod Harmonic Distortion

Most Influential Distortion is the Second and Third

Order

< -50 dBc < -50 dBc< -40 dBc



Distortion Products Increase as a Function of

Fundamental's Power

Second Order: 2 dB/dB of FundamentalThird Order: 3 dB/dB of Fundamental

3

f 2f 3f

Power

in dB

2

f f2f - f1 2 1 2

Power

in dB

33

2 12f - f

Two-Tone Intermod

Harmonic Distortion

Third-order distortion

Second-order distortion



Relative Amplitude Distortion Changes with Input Power

Level

f 2f 3f

1 dB

3 dB2 dB

21 dB

20 dB

1 dB



Distortion Test:

Is it Internally or Externally Generated?

IF GAIN

� No change in amplitude =

distortion is part of input signal

(external)

Change Input

Attn by 10 dB1

Watch Signal on Screen:2

� Change in amplitude = at least some of

the distortion is being generated inside the

analyzer (internal)

RF INPUT

ATTENUATOR


SpecificationsDynamic Range

Noise Sidebands

Dynamic Range Limited By Noise Sidebands

dBc/Hz

Displayed AverageNoise Level

Dynamic Range

Compression/NoiseLimited By

100 kHzto

1 MHz

Dynamic Range for Spur Search Depends on Closeness to

Carrier



Actual Dynamic Range is the Minimum of:

Noise sidebands at the offset frequencyNoise sidebands at the offset frequency

Maximum dynamic range calculationMaximum dynamic range calculation

Calculated from:

� distortion

� sensitivity



+30 dBm

-115 dBm (1 kHz BW & 0 dB ATTENUATION)

MAXIMUM POWER LEVEL

LCD-DISPLAY

RANGE80 dB

-10 dBm

-35 dBm

-45 dBm

INCREASING

BANDWIDTH OR

ATTENUATION

SECOND-ORDER DISTORTION

MIXER COMPRESSION

THIRD-ORDER DISTORTION

SIGNAL/NOISERANGE105 dB

RANGE145 dB

MEASUREMENT

MINIMUM NOISE FLOOR

70 dB RANGEDISTORTION

80 dB RANGE

DISTORTION

0 dBc NOISE SIDEBANDS

60 dBc/1kHz

SIGNAL /3rd ORDER

SIGNAL/ 2nd ORDERSIGNAL/NOISE

SIDEBANDS


FeaturesModulation Measurements: Time Domain (use Zero Span)

LIN

MARKER

10 msec

1.000 X

CENTER 100 MHz SPAN 0 Hz

RES BW 1 MHz VBW 3 MHz SWP 50 msec


FeaturesModulation Measurements: Time-Gating

Envelope

Detector

Video

Filter

GATE

Time-Gated Measurements in the Frequency Domain

Frequency

time

"time gating"


Advanced Measurements with a VNA

• You can use Frequency Offset mode to do swept power OR swept

frequency distortion measurements with a VNA

• The dual-source PNA allows you to do swept TOI measurements

• Lets see how the block diagram works to enable this.


PNA-X Block Diagram – 4 Port Option 419, 423

Test port 3

C

R3

Test port 1

R1

Source

1OUT 2

Source 2

(standard)

OUT 2

Test port 4

R4

Test port 2

R2

35 dB

65 dB

35 dB

65 dB 65 dB 35 dB

65 dB

Rear

panel

A

35 dB

D B

LO

To

receivers

SW1 SW3 SW4 SW2

J11 J10 J9 J8 J7 J4 J3 J2 J1

RF jumpers

Pulse generators

Receivers

OUT 1

Pulsemodulator

OUT 1

Pulsemodulator

1

2

3

4

Mechanical switch


Setting Up FOM

• Activate FOM

• Setup the primary stimulus

• Setup the source(s) & receiver

frequencies

• Choose the range to display on

the X-Axis

• Enable Frequency Offset

FOM is the enabling technology that is the key to many

critical measurements, such as Harmonics and

Intermodulation Distortion


Power as You Like it• Port powers in the PNA can be

controlled together or individually.

• The primary output of each source

in the PNA-X can support both

Internal or Open Loop Leveling.

• Through the use of FOM, one

source can be set to sweep power

while the other sweeps frequency.

State:

•Auto = turn on when dictated by

the parameters in the channel.

•ON = Turn on whenever this

channel is sweeping

•OFF = Turn off whenever this

channel is sweeping


If You Can’t Measure it, Compute It!!

• The Equation Editor is a powerful and convenient tool to add computation results as a new trace to your measurement display.

• Equations can be based on any combination of existing traces or underlying channel parameters or memory traces along with any user defined constants.

• You can use any of the basic operators or choose from an extensive library of functions and standard constants.

• Equations can be stored for later use.


Harmonic Measurements – Setup Example

Use the multiplier to make a quick job

of setting the receiver frequencies for

the desired harmonics


Harmonic Measurement Results• DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz

• Window 1 = Fundamental + 2nd, 3rd, and 4th harmonic absolute levels

• Window 2 = 2nd, 3rd, and 4th harmonics relative to carrier


Harmonic Measurement Results – Swept Power


• Window 1 = Fundamental + 2nd, 3rd, and 4th harmonic absolute levels

• Window 2 = 2nd, 3rd, and 4th harmonics relative to carrierNote: To change from swept frequency to swept power, simply change the sweep type of each channel to power sweep and set the power levels and the CW Frequency. If the frequency is already within the calibrated range of the swept frequency setup, no further calibration is required.


Setting Up the 2-Tone Stimulus & the Receiver

• We will use the Frequency Offset dialog to configure the source

and receiver frequencies:


CW Fixed Power IMD Results• DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz

5th Order

Products


• Channel Setup

– A swept frequency IMD measurement requires multiple channels.

– A Calibration Channel – This is for convenience. It allows for 1 set of

source power calibrations (1 for each tone) and 1 B receiver cal and 1

Enhanced Response Cal [optional] to be later shared among all the other

channels.

– An [optional] channel to measure the device gain at the center frequency

of the IMD sweep.

– A channel to measure the input and output power levels of tone 1.

– A channel to measure the input and output power levels of tone 2.

– A channel to measure the output level of the lower 3rd order product.

– A channel to measure the output level of the higher 3rd order product.

Swept Center Frequency Fixed Power IMD Measurements


Setting Up Channels to Measure the IMD Products

• Channels to Measure the lower and higher 3rd

order IMD products

– Using “Copy Channel” copy the tone 2 channel to a new unused channel.

– In the FOM dialog change the receiver frequencies to measure the lower 3rd

order IMD product. Relative to the primary that is an offset of -1.5 MHz.

– In the Power & Attenuation dialog turn on “Port 1” and turn on “Port 1 Src 2”.

– Change the S11 measurement to “B,1”.

– Follow the same process in a new channel and set the receiver to measure the higher 3rd order IMD product.

MHzimary

imaryimaryIMD

MHzimary

imaryimaryIMD

MHzimaryF

MHzimaryF

MHzgToneSpacin

FFIMD

FFIMD

5.1Pr

)5.(Pr)5.(Pr2

5.1Pr

)5.(Pr)5.(Pr2

5.Pr2

5.Pr1

1

122

212

+=

−−+=

−=

+−−=

+=

−=

=

−=

−=

+

−

+

−

Continued


Setting Up Channels to Compute the IP3

• Computing the 3rd Order Intercept points.

– Input & Output, High & Low IP3 values can be computed based on all the existing measurements in the channels we have already setup.

– Use one of the existing channels (other than the cal channel)* and create enough traces for each of the IP3 measurements that you want. IP3 is typically expressed in dB, so choose S-Parameters as the base trace for your equations.

– Use the equation editor and use the equations on the right for the desired IP3 result. Remember that in the equation editor, each of the variables are referred by trace number in order to user the error corrected result in the equation.

−

+

+

−

−

+

+

+

+

+

+

−

=

=

==

==

=

=

=

=

=

=

=

=

=

=

IM3

OF2 OF1 OIP3

IM3

OF1 OF2 OIP3

Gain

OIP3

IM3

OF2 IF1 IIP3

Gain

OIP3

IM3

OF1 IF2 IIP3

:FormComplex In

IP3 referredoutput Lower OIP3

IP3 referredoutput Higher OIP3

IP3 referredinput Lower IIP3

IP3 referredinput Higher IIP3

tonelfundamentahigher theof levelpower Input IF2

tonelfundamentahigher theof levelpower Output OF2

tonelfundamentalower theof levelpower Input IF1

tonelfundamentalower theof levelpower Output OF1

product IMDorder 3rdhigher theof levelpower Output IM3

product IMDorder 3rdlower theof levelpower Output IM3

-

-

-

-

This is where having an optional gain (S21) measurement at the center frequencies may be useful.

* Equation traces have to be in a channel that has the same number of points as the equation’s constituent traces.


Swept Frequency IMD Measurement Results



Swept Power IMD Measurement Results• DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz

ucb dist test3 - rficrfic.eecs.berkeley.edu/142/pdf/distomeaslect.pdfspectrum analyzer basics lets...

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